FORCE TRANSMISSION BELT COMPRISING A POLYETHYLENE COATING

Abstract

Disclosed is a force transmission belt comprising a belt member that has a base portion (11) and a force transmission zone (12) thereon, and comprising a polyethelene coating (18) on at least one surface of the belt member; in order to increase the service life, the polyethylene coating (18) is subjected to radiation at a dose of 30 to 300 kGy to increase the wear resistance of the coating.

Claims

1. A force transmission belt with a belt structure comprising: a belt body, a force transmission zone, and a polyethylene coating on at least one surface of the belt structure, wherein the polyethylene coating is composed of high density polyethylene (HDPE) and has been subjected to irradiation with a dose of from 30 to 300 kGy in order to increase its wear resistance.

2. The force transmission belt as claimed in claim 1, wherein the polyethylene coating is a layer in a multiple-ply coating structure, and wherein the layer of the polyethylene coating is exterior in relation to the cause of wear.

3. The force transmission belt as claimed in claim 1 wherein the belt structure has a textile overlayer, and the the polyethylene coating (18) is positioned on the textile overlayer.

4. The force transmission belt as claimed in claim 3, wherein the textile overlayer includes an impregnation layer made of a copolyamide.

5. (canceled)

6. The force transmission belt as claimed in claim 1 wherein the polyethylene coating is modified with a friction-reducing additive.

7. The force transmission belt as claimed in claim 1 wherein the polyethylene coating is applied as a film.

8. The force transmission belt as claimed in claim 7, further comprising an adhesion-promoter layer arranged between the film that forms the polyethylene coating and a surface supporting the polyethylene coating.

9. The force transmission belt as claimed in claim 8, wherein the adhesion-promoter layer is a modified polyethylene (PE) layer.

10. The force transmission belt as claimed in claim 1 wherein the polyethylene coating has a thickness ranging from 20 to 400 nm.

11. The force transmission belt as claimed in claim 1 wherein the polyethylene coating has been subjected to irradiation with gamma-radiation with a dose of from 30 to 80 kGy.

12. The force transmission belt as claimed in claim 1 wherein the polyethylene coating as been subjected to irradiation with beta radiation with a dose of from 150 to 300 kGy.

13. The force transmission belt as claimed in claim 1 wherein the polyethylene coating has been rendered antistatic via conductive additives.

Description

[0017] The invention will be explained in more detail below with reference to embodiments depicted diagrammatically in the drawing, where:

[0018] FIG. 1 is a longitudinal section through a toothed belt with a multilayer coating arrangement on the toothed side;

[0019] FIG. 2 is a longitudinal section through a toothed belt with a multilayer coating arrangement on the reverse side of the belt;

[0020] FIG. 3 is a longitudinal section through a toothed belt with a single-layer poly ethylene coating on the reverse side of the belt.

[0021] The force transmission belt depicted in FIG. 1 is a toothed belt 10 of which the belt structure comprises a belt body 11 and a force transmission zone 12. The force transmission zone 12 has teeth 13, between which teeth there are intervening spaces 14 present. Tension members 15, usually composed of metal wires arranged horizontally alongside one another, run within the belt body 11 in the longitudinal direction of the toothed belt 10.

[0022] In the embodiment depict 4 there is a textile layer 16 which covers the surface of the force transmission zone and which is intended to increase the abrasion resistance of the toothed belt 10 in the region of the force transmission one 12. For many applications, polyurethane is an advantageous material for the belt structure. In order to avoid permeation of the tacky polyurethane through the textile layer 16, the latter has a coating of an impregnation layer 17 made of copolyamide, where the copolyamide is applied in such a way that it penetrates to some extent into the textile layer. A polyethylene coating 18 made of HDPE covers the impregnation layer 17, and between the polyethylene coating 18 and the impregnation layer 17 here there is an intervening adhesion-promoter layer 18. The adhesion-promoter layer 19 can be composed of LLDPE and can have been modified in a known manner.

[0023] The thickness of the polyethylene coating 18 is about 100 m, and said coating is preferably applied in the form of an HDPE film and heat-set. The polyethylene coating can, in particular, in the form of the film, have been irradiated with gamma-radiation prior to application, the radiation dose used here being from 40 to 80 kGy, in particular from 60 to 70 kGy, preferably 65 kGy. The polyethylene coating 18 has been modified h the irradiation, in that in particular long polymer chains have been cleaved and an additional crosslinking has taken place. Corresponding modification of the polyethylene coating can also be achieved by beta-radiation, where radiation doses used are preferably higher: up to 300 kGy.

[0024] In the embodiment depicted in FIG. 2, the layers 16, 17, 18, and 19 are present in the same sequence on the surface of the back of the belt, i.e. on the surface facing away from the teeth 13. This embodiment is suitable for withstanding high loading on the back of the belt.

[0025] The embodiments of FIGS. 1 and 2 can, of course, also be combined with one another, and the toothed belt 10 can therefore have the layer sequence 16 to 19 not only on the toothed side but also on the reverse side of the belt. It is moreover possible, of course, that corresponding layers are advantageously also provided to other forms of belt, for example V-belts and flat belts.

[0026] In the embodiment depicted in FIG. 3, the polyethylene coating 18 is likewise present on the reverse side of the belt, but has been applied there directly with the aid of a layer of an adhesive 20, without textile layer 16 and impregnation layer 17.

[0027] In all cases it is also possible that the irradiation of the polyethylene coating 18 takes place after the polyethylene coating 18 has been applied This has the advantage that the PE layer has good flow properties for the application of the polyethylene coating 18 and that the properties, including the flow properties, are not altered until the subsequent irradiation takes place.

Loading Tests

[0028] The usage properties of the belts were tested in that continuous belts with a belt structure and cross sectional profile as shown in principle in FIG. 1 were exposed to high dynamic loading on a 2-pulley arrangement.

[0029] Each run was continued until discernible damage arose on the external polyethylene coating 18. Test rig parameters were kept constant for all of the experiments.

[0030] Test rig parameters: [0031] 2-Pulley system: continuous belt running over two pulleys of identical size; [0032] Pulleys: type G profile in accordance with ISO 13050, each with 25 teeth, pitch 8 mm; [0033] Velocity of pulleys: rotation rate 1000 min.sup.1; [0034] Installed pretensioning: 600 N per side; [0035] Torque 35 Nm; [0036] Belt size: 112 teeth, width 12 mm, pitch 8 mm (8 M) [0037] Cast PU belt with textile overlay and multilayer plastics coating (FIG. 1)

1. Comparative Experiments

[0038] A first series of tests was carried out on belts with an unirradiated HDPE coating 18. The fundamental structure of the coating on the textile overlay 16 was: [0039] Impregnation layer 17copolyamide (40 m) [0040] Adhesion-promoter layer 19LLDPE (from 20 to 60 m) [0041] (on external side) PE coating 18HDPE (from 30 to 100 m)

[0042] In all of the experiments, while layer thicknesses are varied, there was no substantial difference in the maximal running time. In every case, at most 40 hours were required for the high test loading to abrade the edges of the force transmission zone 12 of the comparative belts with unirradiated HOPE coating. Toward the and of the maximal running time here, fragments of the PE coating 18 separated (flaked away) from the belt. The size of the HDPE fragments separated from the belt increased as the thickness of the coating 18 increased.

2. Loading Tests on Belts of the Invention

[0043] The same test rig and the same test conditions were used to test belts which differed from the comparative belts only in that the coating 18 had been irradiated, as stated in the description.

[0044] For these experiments, a coextruded multilayer film made from the films for the layers 17, 19, and 18 had been irradiated from the HOPE side i.e. on the surface of the coating 18 (for layers sequence see under comparative experiments). Production of the belts was otherwise identical with that of the comparative belts. In both cases the coating film composite was heat-set on the textile overlay 16, and a polyurethane belt was cast in a conventional manner against the back of the textile overlay 16.

[0045] Maximal running times achieved under the high test loading by the embodiments of the invention with irradiated coating 18 were from 100 to 150 hours, i.e. from two to three times as long as without irradiation of the external PE coating 18.

[0046] The abrasion resistance of the belt with irradiated exterior coating was therefore shown to have been significantly increased.

[0047] The invention is, of course, just as suitable for force transmission belts produced in continuous form as for force transmission belts produced with free ends.

[0048] Although in particular the present invention is particularly advantageous for force transmission belts with belt structures made of a thermoplastic, or a castable thermoset, polyurethane, it can also be used advantageously for force transmission belts with a belt structure made of any other familiar material.